In a mixed signal environment, switching noise from clocked and discrete-time elements creates noise that couples into sensitive analog nodes, such as of a radio frequency (RF) receiver. Due to the rapid switching, harmonics of the switching frequencies generate frequency domain spurs that can extend across an entire receiver band of interest.
Traditionally, these spur frequencies have been managed by adjusting the clock frequencies so that harmonics of the switching frequencies do not fall on top of the desired signal. For terrestrial TV tuners, the clock frequency can be adapted by up to +/−4%. A drawback of this approach is that digital signal processing (DSP) elements such as filters and mixers need to be adjusted due to the change in sampling rate. This raises costs in area and power, and makes dynamic switching of the frequency difficult.
Dynamic switching refers to changing of a clock frequency at which the receiver operates on-the-fly, while a TV channel processed by a first tuner is being watched. Such change is needed in a multi-tuner scenario when a second tuner's desired channel is impaired by the first tuner's clock harmonics. The difficulty of dynamic switching occurs because the digital datapath has latency. As such, a large number of data samples exist in the datapath at a previous sample rate which, when processed at a new sample rate, causes frequency warping of the signal that can result in visible artifacts.